IBM MiEM78P468L User Manual
EM78P468N/EM78P468L
8-Bit Microcontroller
8
•
Product Specification (V1.5) 02.15.2007
(This specification is subject to change without further notice)
6.1.4
R3/SR
(Status
Register)
(Address: 03h)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
− PS1
PS0 T P Z DC C
Bit 7: Not used
Bits 6 ~ 5 (PS1 ~ 0): Page select bits
PS1
PS0
ROM Page (Address)
0
0
Page 0 (000H ~ 3FFH)
0
1
Page 1 (400H ~ 7FFH)
1
0
Page 2 (800H ~ BFFH)
1
1
Page 3 (C00H ~ FFFH)
PS0~PS1 are used to select a ROM page. User can use the PAGE instruction (e.g.
PAGE 1) or set PS1~PS0 bits to change the ROM page. When executing a "JMP",
"CALL", or other instructions which causes the program counter to be changed (e.g.
MOV R2, A), PS0~PS1 are loaded into the 11th and 12th bits of the program counter
where it selects one of the available program memory pages. Note that RET (RETL,
RETI) instruction does not change the PS0~PS1 bits. That is, the return will always be
to the page from where the subroutine was called, regardless of the current setting of
PS0~PS1 bits.
Bit 4 (T): Time-out bit. Set to 1 by the "SLEP" and "WDTC" commands or during power
up and reset to 0 by WDT timeout.
Event
T
P
Remark
WDT wake up from sleep mode
0
0
WDT time out (not sleep mode)
0
1
/RESET wake up from sleep
1
0
Power up
1
1
Low pulse on /RESET
1
1
×: don't care
Bit 3 (P): Power down bit. Set to 1 during power on or by a "WDTC" command and
reset to 0 by a "SLEP" command.
Bit 2 (Z): Zero flag
Bit 1 (DC): Auxiliary carry flag
Bit 0 (C): Carry flag